1. Field of Invention
The present invention relates to a variable compression ratio control system, and more particularly, to a variable compression ratio control system capable of stably controlling a variable compression ratio apparatus changing a compression ratio of mixed gas inside a combustion chamber according to an operation state of an engine.
2. Description of Related Art
In general, thermal efficiency of a heat engine is increased when a compression ratio is high. Here, the compression ratio is a ratio of a volume of gas, which flows in a cylinder, compressed by a piston, and is represented by “cylinder volume/combustion chamber volume at a top dead center of a piston”. That is, as the top dead center of the piston becomes high, the compression ratio is increased.
In a case of a spark ignition engine, thermal efficiency may be increased by advance of an ignition timing, but there may be a limitation in the advance of the ignition timing considering abnormal combustion, and the like. Accordingly, a variable compression ratio (VCR) apparatus for improving thermal efficiency of the heat engine is demanded.
The variable compression ratio apparatus is an apparatus for changing a compression ratio of mixed gas according to an operation state of the engine. The variable compression ratio apparatus functions to improve fuel efficiency by improving a compression ratio of mixed gas under a low load condition of the engine, and prevent generation of knocking and improve output of an engine by decreasing the compression ratio of the mixed gas under a high load condition of the engine.
As a result of various experiments for a variable compression ratio apparatus in the related art, it is revealed that a change in a distance between a crank pin and a piston pin by using an eccentric bearing achieves high operational reliability. The eccentric bearing is connected with a control shaft by a plurality of links to be rotated so that the top dead center of the piston is changed according to the rotation of the control shaft.
In the meantime, a variable compression ratio control system is a system for controlling the rotation of the control shaft.
The variable compression ratio control system in the related art transmits torque of a motor to the control shaft by using a worm and a worm gear, which are formed to transmit a torque of one shaft to the other shaft between the one shaft and the other shaft disposed at a twisted position with respect to the position of the one shaft.
However, the worm and the worm gear have relatively larger back lash than other gear coupling, and an excessive noise and vibration may be generated due to the back lash. That is, firm gear-coupling of the worm and the worm gear is not easily secured, such that a self-locking function may be weak. Accordingly, driving of the motor for maintaining a position of the control shaft, as well as rotating the control shaft, is demanded. Further, the power transmission of the motor by the worm and the worm gear demands relatively large driving torque, compared to other gear coupling, so that there is a limitation in a decrease in a capacity of the motor.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.